CHEMISTRY COMMUNITY

Nayra Gharpetian 3F

yes anode is always on the left to avoid confusion. this is a typo

Nayra Gharpetian 3F

an intermediate is a product in one step, then consumed as a reactant in the next step. since it goes from being a product to a reactant, it cancels out and is not included in the overall reaction equation

Nayra Gharpetian 3F

1. balance elements other than hydrogen and oxygen with stoichiometric coefficients
2. balance oxygen with H2O molecules
3. balance hydrogen with H+
4. balance charge by adding electrons wherever necessary

Nayra Gharpetian 3F

i don't think we can determine that without that doing experiments and calculations. i'm pretty sure they would tell us which is the slow step in a problem

Nayra Gharpetian 3F

it means that the rate of the reaction is not dependent of the concentration of the reactants. the rate depends on k

Nayra Gharpetian 3F

i think it's easiest to look at it graphically. if you graph ln [A] vs time and you get a straight line with a negative slope, this is first order. If you graph 1/[A] vs time and you get a straight line with positive slope, this is second order. if you graph [A] vs time and you get a straight line w...

Nayra Gharpetian 3F

the problem will have to specify whether it is in acidic or basic solution

Nayra Gharpetian 3F

if a reaction has two steps, the slower reaction will determine the rate of the reaction because the reaction will be limited to how fast the slowest step occurs

Nayra Gharpetian 3F

i think professor lavelle is going to divide the final based on how long we spent on each section. The longer we spent on a section, the larger its portion on the final will be.

Nayra Gharpetian 3F

pKa + pKb= PKw
pH+pOH=14
Ka*Kb=Kw= 1x10^-14
[OH-]*[H+]=1x10^-14

Nayra Gharpetian 3F

this means that the cathode has a greater electron pulling ability. aka the cathode has a greater likelihood of being reduced, which means it is gaining electrons

Nayra Gharpetian 3F

n is the number of electrons transferred. to find this you have to find the balanced half reactions (including the electrons) and from there you can see how many electrons were transferred. that would be your value for n in ΔG=-nFE

Nayra Gharpetian 3F

first fin E°cell using the standard reduction potentials given. then use the equation ΔG°=-nFE°

Nayra Gharpetian 3F

if the oxygen atoms are not balanced we add water molecules to balance it out.

Nayra Gharpetian 3F

if there isn't a metal conductor we need to add Pt(s)

Nayra Gharpetian 3F

If Q<K, the reaction will favor the products. If Q>K, the reaction will favor the reactants

Nayra Gharpetian 3F

they can be on either side but when we represent them on paper with cell diagrams the anode goes on the left and the cathode goes on the right

Nayra Gharpetian 3F

we must include a salt bridge in order to keep both solutions neutral. as the anode loses electrons, cations form. the salt bridge provides anions to keep the solution neutral.

Nayra Gharpetian 3F

Delta G is at standard conditions. standard conditions are 1 atm and 298 K (room temp, 25 degree Celsius)

Nayra Gharpetian 3F

Why does delta S decrease when temperature increases? I understand it in terms of the equation of delta S because temperature is on the denominator, I just don't understand it conceptually. Can someone please explain this?

Nayra Gharpetian 3F

an increase in both volume and temperature results in an entropy increase.

Nayra Gharpetian 3F

positive work means that work is being done to the system while negative work means the system is doing work. the negative value represents the system losing energy

Nayra Gharpetian 3F

this would not be possible because the negative delta S value would make t*delta S positive. therefore, delta G would always be negative

Nayra Gharpetian 3F

yes I had trouble figuring this out until I realized that the right side of the curve was pointing toward equilibrium (delta G is decreasing) so both sides are spontaneous!

Nayra Gharpetian 3F

work would not be 0 because the equation is w= -P* (delta V). The equation does not include delta P so P would just be the constant pressure and delta V would be the change in volume.

Nayra Gharpetian 3F

yes we solve for kc the same way we solve for kp! :)

Nayra Gharpetian 3F

specific heat capacity is the heat capacity in terms of grams present. molar heat capacity is the heat capacity in terms of moles present. it really just depends on what information is given in the problem

Nayra Gharpetian 3F

delta U is change in internal energy. delta U= q+w

Nayra Gharpetian 3F

as everyone said before, the first law of thermodynamics basically states the conservation of energy

Nayra Gharpetian 3F

what is the difference between delta U and delta H?

Nayra Gharpetian 3F

they are not interchangeable. it depends on what information you're given. if you have moles, then you would use molar heat capacity. if you have grams you would use specific heat capacity.

Nayra Gharpetian 3F

a change of 1 degree Celsius is the same as a change of 1 degree in kelvin. the only difference is that kelvin starts at 0 while Celsius starts at -273. so to convert from Celsius to kelvin all you have to do is add 273 to Celsius.

Nayra Gharpetian 3F

you have to check whether the anion or the cation of the salt will the affect the ph. from there you can determine if it's a conjugate base or acid. if it is a base you use kb, and if it is an acid use ka

Nayra Gharpetian 3F

there are several values of R and the only way we know which one to pick is by looking at the units. match the units of the info they give to the units in R

Nayra Gharpetian 3F

when you need to break bonds for the phase change it is endothermic. for example going from a solid to a liquid is endothermic because some bonds have to be broken in order for it to become a liquid. if bonds need to form it will be exothermic.

Nayra Gharpetian 3F

a strong acid has a low pKa value and a large Ka value. a strong base has a low pKb value and a large Kb value

Nayra Gharpetian 3F

if you have x^3 in your equation you can just approximate and say that the value of x is negligible in the denominator. having x^3 prevents you from using the quadratic equation so to solve we have to approximate. I believe our K value has to be less than 10^-4 to approximate but i could be wrong

Nayra Gharpetian 3F

the temperature doesn't rise during a phase change because the energy goes towards altering the molecules and changing the phase. once the phase changes the temperature increases until the substance changes phases again.

Nayra Gharpetian 3F

their equilibrium constants are just very large because the acid/base almost completely dissociates

Nayra Gharpetian 3F

I would wait for professor lavelle to mention it lecture

Nayra Gharpetian 3F

H2O is in excess so the change in concentration would be negligible. if we were to add it into Kw it would be in the numerator and denominator, and therefore would cancel out.

Nayra Gharpetian 3F

basically it says that if there is a change in the system the chemical reaction will "shift" to go back to equilibrium and minimize the effects of that change

Nayra Gharpetian 3F

yes! an ICE table can be used for both partial pressures and concentrations.

Nayra Gharpetian 3F

to find Ka from pKa you would do 10^(-pKa)

Nayra Gharpetian 3F

How would we find the pH of a salt if both the cation and anion affect the pH of the solution?

Nayra Gharpetian 3F

Q uses the concentration values we currently have, but K uses the equilibrium concentrations

Nayra Gharpetian 3F

all the worksheets are different for every UA. go to as many as you can they are so so so helpful!!

Nayra Gharpetian 3F

as everyone said above Kw was experimentally determined

Nayra Gharpetian 3F

yes 1 bar is approximately 1 atm so we say that 1atm=1bar

Nayra Gharpetian 3F

I is initial concentrations, C is change in concentrations, and E is concentrations at equilibrium. Depending on what information we're given, we can use ICE tables to find the K value, or concentrations at equilibrium (if we already know the K value).

Nayra Gharpetian 3F

if both sides of the equation have the same number of moles, a change in pressure will not affect equilibrium

Nayra Gharpetian 3F

Problem 4 says: At a certain temperature, the given reaction has an equilibrium constant of Kp=341

PCl3(g)+Cl2(g)↽−−⇀PCl5(g)

PCl5 is placed in a sealed container at an initial pressure of 0.0220 bar. What is the total pressure at equilibrium?

Can someone explain how to solve this?

Nayra Gharpetian 3F

Q is at any point in the reaction but K is at equilibrium. comparing Q and K can tell you that the reaction is at equilibrium, or whether the reaction will shift to the right or the left to reach equilibrium

Nayra Gharpetian 3F

M is concentration in mol/L. moles will be expressed as mol or mole

Nayra Gharpetian 3F

What's the difference between amphoteric and amphiprotic?

Nayra Gharpetian 3F

omg thank you! this is so so so helpful <3

Nayra Gharpetian 3F

Can someone explain how to determine which substance is amphoteric? Here's the question:

Which of these substances is amphoteric, that is, it can act as a Brønsted acid and a Brønsted base?

BrO2^-
H3PO4
HBrO2
PO4^3-
H2PO4^-

Nayra Gharpetian 3F

flashcards are super super helpful when trying to memorize names, or just learning the concepts. i would definitely say use flashcards for learning the different shapes of compounds, and naming compounds.

Nayra Gharpetian 3F

When do we add -ate to the end of the metal name?

Nayra Gharpetian 3F

When would we use the equation Ka= [A-][H+]/[AH]?

Nayra Gharpetian 3F

hi so you would use the mass percentages and assuming that you have a 100 gram sample we would have 37.5 g C, 12.6 g H, and 49.9 g O. Convert these to moles and find the molecular formula. This will be the formula used to draw the lewis structure and determine the hybridization

Nayra Gharpetian 3F

from my understanding a chelate contains a ligand that forms a ring of atoms that includes a central metal atom. i'm not completely sure why chelates form so if you know please let us know lol :)

Nayra Gharpetian 3F

since each carbon atom has 4 regions of electron density (4 bonds) the shape is tetrahedral

Nayra Gharpetian 3F

Yes! chlorine gas is a diatomic molecule and therefore chlorine gas is Cl2

Nayra Gharpetian 3F

What is a delocalized pi bond?

Nayra Gharpetian 3F

As Dr. Lavelle has mentioned in lecture, H can never be the central atom because it can only have 1 bond

Nayra Gharpetian 3F

having the lone pair in the equatorial plane is more favorable because it only interacts with 2 bonds at 90 degrees. if it was on the axial plane it would interact w/ three atoms.

Nayra Gharpetian 3F

For a structure like this it's more trying different things and seeing which works. I had some trouble on this too but you just have to take different approaches and see which gives you the most stable and correct structure. there are multiple ways to do it

Nayra Gharpetian 3F

How does XeF2 have a linear shape if it has 3 lone pairs?

Nayra Gharpetian 3F

Question 3 says: A Lewis structure is a two-dimensional representation of a molecule that does not necessarily show what shape that molecule would take in three dimensions. Based on the Lewis structure and your knowledge of VSEPR theory, approximate the smallest bond angle in this molecule. I'm not ...

Nayra Gharpetian 3F

What specific characteristic do N, O, and F have that allow them to hydrogen bond with H? Is it just because they are highly electronegative?

Nayra Gharpetian 3F

Hmmmm I'm not 100% sure but I think if we had to use electronegativity values, they would be given in the problem. To my understanding there isn't a chart we should print out but if I'm wrong pls correct me :)

Nayra Gharpetian 3F

yes, a greater atomic radius in LDF makes it more polarizable. In terms of ionic bonds, this means that the bigger the radius of the anion, the easier it is for it to be distorted, which gives it some covalent characteristics

Nayra Gharpetian 3F

Since AsF3 is polar, the bonds are stronger meaning it would require more energy to break the bonds. Therefore it would require a greater melting point compared to a non polar molecule like AsF5

Nayra Gharpetian 3F

Hi can someone explain how to do this problem? I can't seem to get the correct answer. Urea is an organic compound widely used as a fertilizer. Its solubility in water allows it to be made into aqueous fertilizer solutions and applied to crops in a spray. What is the maximum theoretical number of wa...

Nayra Gharpetian 3F

I think finding the formal charges will make it easier to determine if your structure is the most stable form.

Nayra Gharpetian 3F

yeah I would say to just learn the rules for naming the really common formulas. that would really help you during exams and practice problems

Nayra Gharpetian 3F

Is the structure more stable when the formal charges add up to 0, or if they add up to the net charge?

Nayra Gharpetian 3F

lewis acids accept electrons while lewis bases donate electrons

Nayra Gharpetian 3F

Hi could someone explain how to draw the lewis structure for the phosphite ion? I keep getting it wrong and I'm not sure why

Nayra Gharpetian 3F

Hi so the only equation you would need is lambda= h/m x v. For each of the particles given all the values stay the same except their masses. So to find velocity I would reorganize the equation to equal v, v=h/m x lambda. Then the only value that would change based on the particle is the mass, and th...

Nayra Gharpetian 3F

If n=5, then l can theoretically equal 0,1,2,...,n-1

Nayra Gharpetian 3F

Hi I can't figure out how to solve the second part to this problem. The problem says: The E. coli bacterium is about 1.7 μm long. Suppose you want to study it using photons of that wavelength or electrons having that de Broglie wavelength. What is the energy E photon of the photon? What is the energ...

Nayra Gharpetian 3F

Hi ml is referring to the orientation of the angular momentum, (like px, py, pz). Each orientation also refers to an orbital in a subshell. For example, px may refer to the first orbital of the p block. This relates to the spin of an electron because since there are two electrons in each orbital, ea...

Nayra Gharpetian 3F

Yes as everyone said above l correlates to the subshell. if l=1, then we are in the p subshell

Nayra Gharpetian 3F

yes amplitude is only used in the wave model. when light acts like a photon amplitude does not increase the energy. the only way to increase energy would be to increase frequency.

Nayra Gharpetian 3F

I'm pretty sure part A is CuBr2, but either way Megan's steps are correct. If you follow the same steps for part c, (make sure to convert kg of UF6 to g), you should get 430. mol F^- as your answer

Nayra Gharpetian 3F

The Lyman Series ends in n=1 and the Balmer Series ends in n=2. Also, the Lyman Series emits UV light because the gap between n=2 and n=1 is really big. Balmer series emit visible light. So if the problem says that UV light is emitted, you know that it's a Lyman series and that n final= 1. Hope that...

Nayra Gharpetian 3F

yes!! i've noticed that i always make mistakes when i don't write my units throughout the problem. i always make sure to write my units even if it takes a little longer to solve the problem :)

Nayra Gharpetian 3F

Yes we will be given constants, equations, and the periodic table. There are two links Professor Lavelle's website with equations and the periodic table. I would highly recommend printing those out! For studying I would just focus on understanding the constants and equations and when to apply them.

Nayra Gharpetian 3F

yes everyone above is correct. it's basically saying the delta E can be applied to the E=hv equation to solve for frequency.

Nayra Gharpetian 3F

yes the work function is the threshold energy. to find the work function (if they don't already provide it) you would use the equation Ephoton - work function= kinetic energy

Nayra Gharpetian 3F

yes the analogy is a perfect example. the negative sign is to show that the electron is losing energy, but we change it to a positive to calculate for wavelength and frequency, etc. basically to prove the conservation of energy.

Nayra Gharpetian 3F

yes i take similar approaches to everyone above. no matter which approach you take you should get the same answer. a chemical equation only has one correct balanced equation.

Nayra Gharpetian 3F

a black body is an object that emits/absorbs all frequencies of light. however, this is a theoretical concept because no such object exists.

Nayra Gharpetian 3F

That is a great question. In the photoelectric experiment they observed that increasing the intensity of the light did not eject electrons and they concluded that light was not acting like a wave. Instead it was acting like it was made of individual photons, where the individual photon's energy mus...

Nayra Gharpetian 3F

Yes! This is a super important concept to understand when trying to find the amount of product produced. This is why knowing how to balance an equation and converting between mols and grams is a key concept. Thanks for this great explanation.

Nayra Gharpetian 3F

Thank you for these great acronyms! This will be super helpful when working with prefixes. :)

Nayra Gharpetian 3F

I did this post assessment module a few days ago but if I remember correctly I got it right using these steps: Convert the 5.00 g KMnO4 to mols using its molar mass (158.04g/mol) and you'll get 0.0316 mol. Then using the volume you're given, find the molarity of the solution. Make sure to change th...

Nayra Gharpetian 3F

I did this post assessment module a few days ago but if I remember correctly I got it right using these steps: Convert the 5.00 g KMnO4 to mols using its molar mass (158.04g/mol) and you'll get 0.0316 mol. Then using the volume you're given, find the molarity of the solution. Make sure to change the...

Search found 101 matches